The 14,000 locals left homeless by the two quakes were shaken overnight by about 60 aftershocks. At the end of a day spent sifting through debris, rescuers said three people had died in Cavezzo, three in San Felice sul Panaro, four in Mirandola, one in Novi di Modena, four in Medolla and one in Concordia.

Most of the victims were employees at factories that collapsed just after they had reopened after the first quake. The area produces medical products, tiles, machine tools, cheese and sports cars.

The death toll prompted claims that factory owners and the authorities had failed to ensure that their facilities were safe before reopening.

Three employees of one firm, BBG in Mirandola, which had been given permission to reopen on Monday, were killed when the building collapsed.

In San Felice sul Panaro, colleagues of a Moroccan man, Muhammad Azeris, said he had been forced back to work at a factory after the first quake, under threat of losing his job. He was one of three employees who died when the factory crumbled on Tuesday.

"I think that an investigation will need to be opened here to check who cleared as safe these companies – to understand who is responsible for this," a union official, Erminio Veronesi, said.

Rules on strengthening buildings in the area against earthquakes were toughened up in 2003, suggesting that factories built previously may have been vulnerable.

The farming group Coldiretti said the two quakes had caused €500m (£400m) in damage to local agriculture, while the Modena chamber of commerce estimated that the first earthquake alone had cost businesses €1.5m.

Experts continued to assess the damage to the area's churches and historic buildings, which a culture ministry official, Antonia Pasqua Recchia, called "disastrous and dramatic". In the Mantua area, 100 out of a total of 300 churches had collapsed or been damaged, he said.